Resonant circuit assembly



Feb. @45 a. ha MMSQN M RESQNANT CIRCUIT ASSEMBLY Filed Aug. 15, 1945 i Sheets-Sheet l Feb. 17, -19487 R. vH. MAxsoN RESONANT CIRCUIT ASSEMBLY Filed Aug; 16, 1943 4 Sheets-Sheet 2 Feb. 1.7, 1948. R. H. MAxsoN RESONANT CIRCUIT ASSEMBLY Filed Aug 16, 1943 4 Sheets-Sheet 3 Feb. 17, 1948. n.11. MAxsoN RESONANT CIRCUIT ASSEMBLY Filed Aug. 16, 1943 4 Sheets-Singt 4 Patented Feb. 17, 1948 RESONAN T CIRCUIT ASSEMBLYv Rolland H. Maxson, Milton, Wis., assigner to The Burdick Corporation, Milton, Wis., a corporation of Delaware Application August 16, 1943, Serial No. 498,856

(Cl. Z50-16) 9 Claims.

1 The present invention relates to improvements in resonant circuits, oftentimes called tank circuits, and has for its primary object the provision of a, new and improved circuit assembly especially suited for high frequency apparatus, such for instance, as the final amplifier of a high frequency therapeutic apparatus. Apparatus of this character is disclosed and claimed in my copending application Serial No. 492,251, filed June 25, 1943.

The final amplifier disclosed in my copending application is featured by a plate tank circuit having a. very high full load effective Q, i. e., the condenser of the tank circuit has a high capacitance, and the present invention provides a. new and improved tank circuit assembly characterized by a condenser of the character specified.

One of the objects of the present invention is to provide a condenser-coil assembly comprising a condenser, and especially a condenser of large capacitance and operable at high voltage, having desirable physical characteristics, such for instance,v as small size, short length, of a shape that is especially suited for therapeutic equipment, and which is of rugged construction.

A further object of the present invention is to provide a new and improved tank circuit assembly utilizing metallic mounting plates constructed and arranged to form part of the condenser and which are symmetrical and capacitatively balanced to ground.

Another objectv of the present invention is to provide a new and improved tank circuit assembly including a trimmer condenser supported by and electrically connected to the supporting means for the main condenser and an inductance coil.

Another object of the present invention is to provide an improved circuit assembly wherein the inductance coil is secured to the condenser in an improved fashion.

A further object of the present invention is to provide a new and improved tank circuit assembly wherein the condenser and inductance coil are symmetrically located and balanced with respect to ground and to the tubes associated therewith.

Another object of the present invention is to provide a new and improved tank circuit assembly which may be readily mounted in close proximity to a pair of tubes operated in push-pull and in the plate circuit of which the assembly is connected.

A further object is the provision of a new and improved tank circuit assembly, including metallicmounting plates and supports mounted on insulators insulating it from a chassis, in which the direct current plate supply voltage is connected to the metallic plates and supports.

Other objects and advantages of the present invention will become apparent from the ensuing description, in the course of which reference is had to the accompanying drawings, in which Fig. 1 is a top plan view of a final amplifier assembly for a therapeutic apparatus in which the present invention is embodied;

Fig. 2 is a side view of the assemblythe tubes being shown in phantom;

Fig. 3 is an end view of the same;

Fig. 4 is an enlarged vertical cross-sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 is a fragmentary cross-sectional detail taken along the line 5-5 of Fig. 2; and

Fig. 6 is a schematic illustration of the nal amplifier circuit in which the present invention is embodied.

Referring first to Fig. 6, it may perhaps be well to note that the circuit illustrated in this figure is illustrated and features thereof claimed in my copending application referred to above. This circuit is the final amplifier circuit and it includes an input transformer of which only the secondary winding I0 is illustrated. The amplifier output is inductively supplied to a patients circuit coupling coil l2, which may be adjustable relative to a plate tank circuit assembly constructed and arranged in accordance with the present invention.

The plate tank circuit assembly of the present invention includes a two-part inductance coil M, a condenser I6 of the fixed air spaced type, and a trimmer condenser i8 also of the air spaced type and preferably constructed to have' but a limited range of adjustment.

The input winding l0 forms part of a grid tank circuit including also a dual section variable air spaced condenser 2D, the movable rotor of which is connected to a chassis to be described in greater detail hereinafter. The terminals of the grid tank circuit are connected by conductors 22 and 24 to the grids 26 and 23 of electron tubes 30 and 32, respectively. The nal amplier, including the tubes 39 and 32, is operated as a class C amplii'ler. The lamentary cathodes 34 and 36 are connected in parallel by conductors 38 and to a suitable source of current. A radio frequency j by-pass condenser 40 is connected across the conductors 38 and the separate conductors are connected to the chassis by the radio frequency byypass condensers 42 and 44, symmetrically arranged relative to the conductors. These condensers provide return circuits for the Yradio frequency grid and plate currents and keep the laments at ground for radio frequency currents.

Grid bias is supplied to the grids of the amplier tubes 30 and 32 by grid leak resistor 46 connected to one of conductors 38 and to the center tap of coil I0. A rectified radio frequency grid current flows through the resistor 45 thereby setting up a direct current voltage providing bias for the grids.

The final amplifier includes also the plate tank circuit having a very high full load effective Q and comprising the coil I4 and condensers I3 and I8, previously referred to. The plate tank circuit is connected to the anodes 48 and 50 of tubes 30 and 32 through conductors 52 and 54.

Neutralization of the amplifierv is effected through variable condensers 56 and 58 connected to the grids of the tubes (through conductors |68 and |70) and through conductors 60 and 62 to the plate tank circuit. Y

Plate voltage for the tubes is supplied from a suitable source through a conductor 64 connected to the mid point of coil I4 and having interposed therein a radio frequency choke coil 66. A bypass condenser 68 serves, together with coil 66, as a lter to isolate the direct current plate voltage from the radio frequency voltage. The con-l -denser 68 also maintains the plate circuit at ground potential with respect to radio frequency and it is symmetrically located relative to condensers 42 and 44. The fixed plates of the condensers I 6 and I 8 are connected to each other and by conductor 'I0 to the voltage supply line 64 so that there is no high direct current potential between the condenser plates and so that the only voltage across the condenser plates is the radio frequency voltage appearing across the tank circuit.

The present invention pertains Yto the construction andv arrangement of the plate tank circuit including ,primarily the coil I4 and the condensers I6 and I8 together with the supply of the plate voltage to the amplifier. This construction is illustrated in Figs. 1 to 5, inclusive, to which reference is now had. 1 The tank circuit assembly includes, as heretofore indicated, the two-section inductance coil I4, the xed condenser |6, and the adjustable trimmer condenser |8, which are supported upon a metallic 'chassis including a generally U-shaped and inverted portion |00 secured as by bolts to a wider base portion |02. The base portion |02 may be provided with anges |04 at its ends so that it may be readily secured to a metal cabinet or the like housing the apparatus.

The coil I4 is formed of copper tubing and in two sections separated by a centrally generally horizontal portion |06. Each section consists of slightly less than three turns (a total of about 5% turns). The ends |08 of the coil are extended downwardly in symmetrical fashion so that the coil may be secured to and supported by the condenser I6. The downwardly extending portions |08 are pinched, as indicated by reference character .I I0, to provide good supports for tubular terminal carrying extensions ||2. 'I'he extensions ||2 extend inwardly to a plane passing vertically through the axis of the coils so that the conductors 52 and 54 may be led symmetrically to the tubes 30 and 32. Terminal clips ||4 are -secured to the conductors 52 and 14 so that con-l nections may readily be made to the plate or anode terminals at the tops of the tubes 30 and 32. The fixed condenser I6 comprises a plurality of spaced apart plates, alternate ones of which secured together in electrically conductive manner. One set of plates isY constituted by the two indicated by reference characters I I6, and the other by the two indicated by reference characters ||8. The plates, which are circular in configuration, are each provided with two pairs of diametrically opposite apertures |20, through which pass metallic conductive supports for the other set. Thus, the two plates IB are mounted on diametrically opposite supports |22 extending through apertures I2|2l in the two plates ||8. The plates ||8 are mounted upon the diametrically opposite supports |24 passing through the apertures |20 in the plates |IB. lThe plates may be secured to the supports in suitable manner, as by nuts and vtubular spacers |26.

The inductance coil I4 is supported by the two uppermost supports |22 and |24, the ends of the coil being spaced by tubular spacers |20. In order to secure good `contact between the various plates and ends of the coil, the plates, coil ends and spacers may be integrally secured together, as by brazing, welding, or the like.

The plate and coil subassembly is mounted upon a supporting structure including pairs of conductive metallic plates |28 and |30 and avplurality of insulating strips |32 arranged in the form of a square. The strips are secured relative to each other and the metallic plates by bolts |34, and the plates are spaced from the strips |32 by spacing washers |35, which may be of metal, ber, or the like. The insulating strips |32 are made of Mycalex. The construction of the strips of insulating material minimizes the amount of insulating material used thereby to minimize the electrical losses at the high frequency at which the amplifier is operated, i. e., 13.66 megacycles. While the amount of insulation has been minimized, the illustrated and described construction is quite rugged. The small washers |35 used to space the insulating bars from the metal mounting plates |28 and |30 increase the leakage path across the insulating strips, extending from the condenser supporting rods |22 and |24 to the mounting plates |28 and |30. The condenser plate supports |22 and |24 extend through the strips, and the plates |28 and |30 are cut away as indicated by reference characters |36 to provide suitable clearance between the supports and plates. The clearance thus provided andalso the clearance provided by apertures |20 in the condenser plates is suiiicient for the radio frequency voltage appearing across the'condenser plates.

The tank circuit assembly thus far described is supported upon the chassis |00 by means of generally vertically extending brackets |38 and |40 secured to the metallic plates |28 and |30, respectively. Brackets |40 are bent at right angles and extended horizontally to support the trimmer condenser I8. The brackets are secured to the assembly so that the metallic plates and the insulating strips, which have a generally square configuration, are supported with one diagonal of the square vertically disposed.

The tank circuit assembly is insulated from the chassis by steatiteinsulators |42 through which pass fastening bolts |44, as best illustrated in Fig. 4.

The trimmer condenser I8 is of the split stator type. The stator sections are supported by porce-I lain end plates |48, the outer ones of which and the rotor |48 of the condenser are supported Vupon metallic brackets |50, suitably secured to the ex- 5 tended portions of the main assembly supporting brackets |40. The stator sections of the trimmer condenser are connected by conductors |52 to the lowermost condenser plate supports |22 and |24.

The trimmer condenser is adjustable through a limited range by means of an adjusting arm |54 made of insulating material and extending through an aperture in a slide plate |56 adapted to be moved vertically a limited distance upon vertical support |58 secured to chassis |08. The extent of movement is determined by a vertical slot (not shown) in the slide plate |55 adapted to receive a screw |00. When the screw |60 is loosened, the slide plate may be moved vertically a distance not greater than the length of the slot therein.

The tank coil assembly of the present invention is such that the direct current plate voltage need not be connected across the condenser I6. The plate voltage is supplied to the assembly through the conductor 64 connected to the lower terminal of the choke coil 65 and by conductor 'I0 to the metallic supporting brackets and conductive plates |28 and |30. The choke coil 65 is supported along a vertical diagonal of the square defined by the metallic conductive plates and its upper end is connected by the conductor |62 to the center of the horizontal portion |85 of inductance coil. The upper end of the choke coil is supported by an insulator |64.

The assembly is symmetrically grounded for high frequencies through the previously referred to condenser 68 secured to the lower corner of conductive plates |28 and to the chassis |00, as best illustrated in Fig. 3.

The assembly is compact so that it may be readily located between the two tubes 30 and 32,

which are mounted upon the chassis |02 in suitable tube sockets ISE. Furthermore, the construction is symmetrical as a whole so that the electrical circuits are symmetrical and balanced both with respect to the tubes and to ground, i. e., the chassis or any other surrounding object at ground potential insofar as radio frequency voltages are concerned.

Another advantage of the construction is that the tubes can be placed very close to the tank assembly whereby short electrical connections can be used. rIhe connections 52 and 54 to the anodes of the electron tubes are very short (note Fig. 2) as are the leads |88 and |10 leading from the neutralizing condensers 55 and 58 to the grids of tubes 30 and 32, respectively. Upon reference to Fig. 1, it may be noted that the neutralizing condensers are also mounted on the chassis to one side of the tubes and are shielded from the tubes by vertically extending metallic partitions |12 secured on the chassis |02. The neutralizing condensers may also be readily connected to the plate tank circuit through the conductors 50 and B2 leading to the stator portions of the trimmer condenser |8, as best illustrated in Fig. 1. These connections S and |52 leading from the y neutralizing condensers to the plate tank circuit -at the same time providing satisfactory neutralization of the amplifier. Parasitic oscillation will result if the above mentioned conductors are too long because these conductors act as an oscillatvthe plate connection path of the neutralizing condensers passes through the trimmer condenser as well as the main condenser before reaching the anodes of the electron tubes. It has been found that the length of the connections 60 and 62 between the neutralizing condensers and trimmer condenser is important in the prevention of parasitic oscillation.

The construction of the chassis in two parts, and particularly with an upper part of an inverted U-shape, enables the input side of the amplifier to be located near the output side, and yet be shielded from it. Referring now more particularly to Fig. 3, it may be noted that the input coil l0 is located between the two portions of the chassis alongside the adjustable condenser 20. The grid leak resistor 46 is secured to the underside of chassis |02, as is the condenser 40 heretofore referred to. The condensers 42 and 44 are also symmetrically located relative to the assembly as best shown in Fig. 1. They are connected across the filaments of tubes 30 and 32 of the chassis |00.

Although the present invention has been described in connection with the details of one embodiment thereof, it should be understood that such details are not intended to be limitative of the invention except insofar as set forth in the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent of the United States is:

1. In apparatus of the character described comprising electronic devices including anodes and operated in push-pull supported on a metallic chassis and having a resonant circuit in their anode circuit, said resonant circuit comprising a condenser including in combination, a plurality of spaced apart condenser plates, each having an aperture, means including conductive supports for alternate condenser plates extending through apertures in the other alternate condenser plates for securing said condenser plates in assembled spaced apart relation, means for connecting the supports to the anodes of the devices, insulating supporting structure at opposite sides of said plate assembly for supporting said plates, metallic plates secured to said insulating supporting structure, means for connecting said metallic plates to the source of anode voltage, said metallic plates being cut away to provide spacing therebetween and said Supports, and insulating means for supporting said metallic plates on said chassis.

2. In apparatus of the character described comprising electronic devices including anodes and operated in push-pull supported on a metallic chassis and having a resonant circuit in their anode circuit, said resonant circuit comprising a condenser, including in combination, a plurality of spaced apart circular condenser plates, each having a pair of diametrically opposite apertures, means including electrically conductive supports connected to alternate condenser plates and at points symmetrically located relative to the apertures and extending through the apertures in the other alternate condenser plates for securing said condenser plates in assembled spaced apart relation, said supports extending beyond the outermost plates, means for connecting said supports to the anodes of said devices, insulating strips arranged in the form of a square and located at opposite sides of the condenser plate assembly, said strips being individually secured centrally thereof to opposite ends of said supports, metallic plates secured to said insulating strips, said metallic plates being substantially square and of a 7 size substantially equal to that bounded by said strips, said metallic plates also being cut away along their edges to space them from the supports passing through said strips, means for connecting said metallic plates to the source of anode voltage, and insulating means for supporting said metallic plates on said chassis.

3. A condenser assembly for mounting on a chassis and for connection to a source of anode voltage, including in combination, a plurality of spaced apart condenser plates, each having an aperture, means including supports for alternate condenser plates extending through the apertures in the other alternate condenser plates for securing the condenser plates in assembled spaced apart relation, insulating supporting structure at opposite sides of said condenser plate assembly for supporting said plates, metallic plates secured to said insulating structure, said metallic plates being cut away to provide spacing therebetween and said supports, metallic supporting brackets secured to said metallic plates and supporting said metallic plates symmetrically relative to the chassis, a trimmer condenser having a split stator and a rotor supported by metallic end supports insulated from the stator and conductively supported on said brackets, means symmetrically 1ocated relative to the assembly for capacitatively connecting said metallic plates to the chassis, and means for connecting said metallic plates to the source of anode voltage.

4. A condenser-coil assembly, including in combination, a plurality of spaced apart condenser plates, means including supports for alternate plates extending in spaced relation to the other al-Y alternate plates for securing said plates in two sets that are disposed in spaced apart relation, and a helical inductance coil made of tubular material symmetrically located relative to said plates, the opposite ends of said coil being secured at opposite ends of said plate assembly to the plate supports for the two sets of plates.

6. A condenser-coil assembly, including in combination, a plurality of spaced apart circular condenser plates each having a pair of diametrically opposite apertures, means including supports for alternate plates extending through apertures in the other alternate plates and attached to said rst mentioned alternate plates symmetrically relative to the apertures for securing said plates in two sets, disposed in spaced apart relation, insulating strips through which said supports extend and metallic plates secured to the strips for supporting said condenser plates, and an inductance coil symmetrically located relative to said condenser and metallic plates, the ends of said coil being secured at ends of said plate assembly to portions of plate supports for the two sets of plates located between the assembly and the insulating strips.

7. A condenser-coil assembly adapted to be supported on a metallic chassis and to be connected to an anode voltage source, including in combination, a plurality of spaced apart circu- 8 lar condenser plates each having a pair of d1- ametrically opposite apertures, means including supports for alternate condenser plates extending through apertures in the other alternate condenser plates and attached to said iirst mentioned alternate condenser plates symmetrically relative to the apertures for securing said condenser plates in two sets disposed in spaced apart relation, insulating strips through which said supports extend and metallic plates secured to the strips for supporting said condenser plates, an inductance coil symmetrically located relative to said condenser and metallic plates, the ends of said coil being secured at the ends of said plate assembly to portions of the plate supports for the two sets of plates located between the assembly and the insulating strips, means symmetrically located relative to the assembly of plates and coil for capacitatively connecting said metallic plates to said chassis, and means for connecting said metallic plates and the mid point of said coil to said anode voltage source.

8. In apparatus of the character described comprising a metallic chassis, and a pair of electron tubes mounted on the chassis and operated in push-pull and supplied with anode voltage from a direct current voltage Source, a condenser-coil assembly including in combination, a

plurality of spaced apartA circular condenser plates each having a pair of diametrically opposite apertures, means including supports for alternate condenser plates extending through apertures in the other alternate condenser plates and attached to said rst mentioned alternate condenser plates symmetrically relative to the apertures for securing said condenser plates in two sets disposed in spaced apart relation, insulating strips through which said supports extend and metallic plates secured to the strips for supporting said condenser plates, an inductance coil symmetrically located relative to said condenser and metallic plates, the ends of said coil being secured to the ends of said plate assembly to portions of the plate supports for one of the two sets of plates located between the assembly and the insulating strip, said strips being disposed in the form of a square and said metallic plates being substantially square in form, insulating means supporting said assembly in the chassis with the square disposed with a diagonal substantially vertically and the coil above said plate assembly and so that said tubes are located one at each side of the assembly alongside the condenser plates, means connecting the ends of said coil to the plates of the tubes, means including a condenser symmetrically located relative to the assembly of plates and coil for connecting the metallic plates to said chassis, and means including a second inductance coil supported adjacent the vertical diagonalsof said plate assembly and connected at one end to the metallic plates and voltage source and at its other end to the mid point of said rst inductance coil for supplying anode voltage to the tubes.

9. In apparatus of the character described comprising a pair of spaced apart electron tubes operated in push-pull, a condenser-coil assembly including in combination, a plurality of spaced apart condenser plates each having an aperture, means including supports for alternate condenser plates extending through apertures in the other alternate condenser plates for securing said condenser plates in two sets disposed in spaced apart relation, an inductance coil symmetrically located relative to said condenser 9 plates, the ends of said coil being supported at the ends of said plate assembly by the support'l for the two sets of plates, and means supporting said assembly symmetrically between said tubes with the condenser plates and coil bet-Ween the tubes and said coil above the tubes with its axis disposed lengthwise relative to the spacing of the tubes.

ROLLAND H. MAXSON.

REFERNCES CITED` y The following references are of record ih the le of this patenti UNITED vSTATES PATENTS Number Name Date 1,725,060 Davis s Aug. 20, 1929 1,880,568 Weir et al Oct. 4, 1932 2,155,786 Fisoher Apr. 25, 1939 Number Name Date Lindberg Jan. 18, 1938 Proctor June 2l, 1927 Dubiler May 6, 1930 Smith Apr. 24J 1934 Cramer July 9, 1940 Usselman Mar. 12, 1940 Barry Aug. 29, 1939 Ditcham Jan. 18, 1927 Kolster Nov. 5, 1935 Muth Feb. 25, 1936 Leach Dec. 4, 1934 Usselman July 6, 1937 OTHER REFERENCES Vacuum Tubes As High Frequency oscillators, The Bell System Technical Journal, vol. XIV, January 1935, pp. 97-134. 

